ESCA and static SIMS have been used to examine the surface rearrangement that occurs upon hydration and dehydration of phase-separated copolymers comprised of hydrophobic [styrene, octastyrene, isoprene, isopropyl methacrylate (IPMA), etc.] and hydrophilic [hydroxyethyl methacrylate (HEMA), dihydroxypropyl methacrylate (DIMA), methyacrylic acid (MAA) etc.] blocks. The degree of surface enrichment observed for a given component will depend upon a variety of items including casting solvent, temperature, phase separation, and the environment the sample is exposed to. Typically for block copolymers prepared by casting in air the hydrophobic segment is surface enriched. Reversal to surface enrichment of the hydrophilic component is usually observed after the sample is soaked in water then freeze-dried under UHV conditions. The degree of reversal depends on the type of hydrophobic and hydrophilic blocks, their block lengths, and the number of blocks in the copolymer. Two systems recently examined were styrene-DIMA and IPMA-MAA. The styrene-DIMA diblock system exhibited significant restructuring upon hydration and dehydration. Both diblock and multiblock IPMA-MAA samples exhibited little, if any, surface enrichment of MAA after soaking in water at room temperature. Some restructuring was observed for the diblock IPMA-MAA sample after exposing it to boiling water. Experiments are currently underway to examine the IPMA-MAA system in more detail using trifluoroethanol to derivatize the acid groups of MAA.